At present, optical sensors are manufactured using CCD 30 (Charge Coupled Device) technology. However, these sensors have disadvantages caused by a not always satisfactory reading performance, complexity, cost and size of the entire reading device.
Furthermore, for the manufacture of optical sensors it has already been proposed to use the CMOS technology, presently employed only in integrated electronic circuits. Hitherto. however, CCD technology has been preferred to CMOS technology, since its performance is better as to quantic efficiency, optical “fill factor” (i.e. the fraction of the useful area occupied by the individual detection element or pixel in order to acquire optical data), dark current leakage, reading noise and dynamics.
Recently, active pixel CMOS sensors (with an amplification section inside the pixel) have been developed, which have performance levels competitive with CCD sensors, but far greater functional capabilities. An image acquisition device can be divided into two parts, i.e. a (linear or matrix-type) optical sensor, supplying output electric signals correlated to the received light, and a unit for processing the electric signals. With the CCD technology used hitherto, whenever the processing unit has to collect data from the optical sensor it must access all the pixels forming the optical sensor in a predetermined sequence. On the other hand, CMOS technology allows the processing unit to access any pixel directly, without having to comply with a specific order, and without the need to access all the existing pixels. In addition, CMOS sensors are fully compatible with logic circuits produced using CMOS technology itself.